The present invention relates in general to wind-driven power generation devices, and more particularly to a tower for supporting a windmill rotor.
Windmills have been known since ancient times. They extract power from the wind and usually the power is used in driving pumps for irrigation or to supply electrical power in rural areas. With the recent increase in energy costs, the attractiveness of wind power has improved.
Recently, consideration has been given to using wind power generators to supply electrical energy for utilities as an alternative to conventional electrical generation plants, hopefully to reduce the amount of costly fuel oil which is now used. However, windmills capable of generating sufficient power to provide a meaningful alternative source of energy are faced with a host of problems.
Wind conditions can vary widely. Wind can vary from geographic location to geographic location and from season to season. Some areas have a considerable amount of wind, while others are wind poor. Wind velocities and direction can fluctuate broadly in short periods of time. In areas where considerable wind exists, the diurnal changes in wind velocity can vary from almost nothing to a considerable value. A mean wind speed is often attendant with frequent gusting and lulls. The wind velocity can vary considerably in elevations close to ground.
A considerable amount of power exists in wind at high speeds. It can be desirable to locate windmills used for commercial power generation in areas having high wind speeds in order to maximize power generation output. A tower must be designed to avoid damage during high winds. In the past, windmill towers have been destroyed by the extremely high forces produced by high winds.
The present invention provides a windmill tower that can adapt well to varying wind conditions and can withstand high wind forces. As a result, the windmill can be used for large scale power generation. The windmill tower and propeller described in this application are large by windmill standards. The wind turbine will produce a rated three million watts of power in a 40 mph wind. It includes a 3-bladed upwind propeller with a diameter of 165 feet that will stand nearly 200 feet tall at the point of the highest blade rotation. The tower for supporting the rotor is mounted on a concrete and steel base. The entire tower structure and propeller pivot relative to the base as the propeller maintains a position upwind of the tower.
The rotatable tower makes it possible to use a large propeller that, in turn, generates a large amount of power. In most windmills the tower is fixed and the propeller pivots relative to the tower with changes in wind direction. The fixed tower should have a relatively wide base for properly supporting the weight of the propeller and its attendant rotating machinery. If the propeller pivots relative to a fixed tower, and if the tower has a wide base, the propeller blades are usually relatively short to avoid contact with the tower as the propeller changes direction with the wind. Silo towers also have been used, but they generally experience resonance problems and therefore have not proved suitable for large scale power generation applications. The rotatable tower of this invention is a wide base structure that supports the propeller blades at the side of the tower. Since the tower and propeller pivot together with changes in wind direction, the propeller blades do not contact the tower, and therefore long propeller blades can be used.
A windmill tower can be damaged or even destroyed by excessively large resonant vibrations during high wind conditions. In the windmill of this invention, the propeller operates upwind of its tower. There are three primary forces acting on the tower when the propeller rotates upwind of the tower. (1). As the blades of the rotating propeller pass the tower, the tower is cyclically excited by a cyclic thrust loading which tends to push and pull on the tower. (2). The cyclic thrust force of the wind against the propeller blades during varying wind conditions also tends to push and pull on the tower. (3). The tower is subject to cyclic torque loading from the rotating propeller, rotating machinery, and horizontal movement of the wind which produces a twisting or torsional moment in a horizontal plane on the top of the tower.
This invention provides a windmill tower structure having a stiffness that resists cyclic thrust and torque loading on the tower sufficiently to reduce resonant vibrations of the tower to an extent that the tower can safely support the propeller under high wind conditions while generating sufficient electrical power for electrical utility purposes.